I use Babyworld too. That's the first site I found and I use the antenatal club quite a bit, and occassionally the other discussion forums.
I used to go on Raising Kids too but at one point it got a bit too clicky and sometimes a bit 'nasty' to some posters. I found out about Mumsnet from there. I don't visit that site now at all.
I use Mumsnet most; in fact it is my home page on my computer
I use the same name on all sites I visit. It is the first bit of my e-mail address. I am rubbish with remembering usernames that's why I have it!